If you've been hiding out in the lab, constantly checking your March Madness bracket, or escaping the cold to find any ounce of warmth (like me!), chances are you may have missed some exciting news. March turned out to be quite a busy month in the Adaptive Optics world, so here’s what you missed:

1. Exoplanet imaging in under a minute

At the recent AAAS 2015 annual meeting, Bruce Macintosh from Stanford University and Principal Investigator for the Gemini Planet Imager (GPI), discussed that there are over 1,000 confirmed planets due to the help of Adaptive Optics. In order to start really understanding a planet and its characteristics, you need to look at the composition of its atmosphere. Astronomers have relied heavily on the adaptive optics technique, allowing for distortion correction of the atmosphere using a deformable mirror. This has had proven success in regards to GPI, which uses a BMC deformable mirror (4K-DM), as part of its adaptive optics system. It can image planets in about a minute, which used to take up to an hour! GPI recently imaged the HR8799 star system, with three orbiting planets. Since November 2013, GPI has imaged 600 stars and identified 50-60 new planets.

2. 2nd quadruple star system discovered

More exciting news from the Astronomy world was the discovery of a massive planet with a quadruple star system only 125 light-years from Earth. Discovered by the Jet Propulsion Laboratory, they were able to detect the fourth star after fitting the telescopes at the Palomar Observatory with a Robo-AO adaptive optics system. Utilizing the AO technique allowed astronomers to pick up on the faint star that couldn’t be seen before. Below is a diagram illustrating the discovered Ari 30 alongside its pair in a binary systems. Before this detection, only one other planet in a quadruple star system had been discovered before. More sightings are being predicted as exoplanets are found, with the help of Adaptive Optics systems of course!

(Photo credit: NASA / JPL-Caltech)

3. The most valuable brains

Congratulations to Scientists Winfried Denk, Arthur Konnerth, Karel Svoboda and David Tank for being awarded the world’s most valuable neuroscience prize, The Brain Prize, for the invention and development of two-photon microscopy! Two-photon microscopy is helping researchers to understand the human brain and how its networks process information, such as nerve cell communication. It has also enabled the study of nerve cells that control vision, hearing and movement. Recent work has been carried out to implement adaptive optics systems on two-photon microscope systems around the word, including locations such as the Howard Hughes Medical Institute, Institute Langevin at CNRS and Boston University. Standing on the shoulders of giants to improve imaging of the brain with AO!

Now that you are caught up with some of the biggest achievements using Adaptive Optics this past month, check out all of our deformable mirror products that are used in AO instruments like GPI on our website. Questions? Looking for a deformable mirror that will fit your needs? Contact BMC here.

AO 101 Whitepaper

Looking to learn more about Adaptive Optics? Download our whitepaper to learn the fundamentals and how our customers are implemeting our DM's into their AO systems.

Ajou University in Korea has recently reported on femtosecond scanning photocurrent microscopy using our Optical Modulator devices. In this application Ti:Sapphire lasers were divided into pump and probe beams, then focused on the samples using an objective lens, while a pair of two-axis steering mirrors were used to manipulate the positions of both focused laser spots. Our optical modulator was then used to modulate the probe pulse at 20 kHz to capture the photocurrent generated by the probe pulse signals and filter out the photocurrents generated directly by the pump pulse. It is noted in their paper that “this modulator is advantageous over the acousto-optic types because it is free from the dispersion effects and delivers better spatial resolution for the focused laser”. Figure 1 shows the setup of the experiment.

Dr. Meng Cui at the Howard Hughes Medical Center has recently pioneered Super Penetration Multi-Photon Microscopy (S-MPM) at the Cui Lab. He has successfully reported on focusing light through static and dynamic strongly scattering media using our segmented 492-DM (See more on the application here). By using the iterative multi-photon adaptive compensation technique (IMPACT), he since reported new results on in vivo fluorescence microscopy, providing a unique solution to noninvasive brain imaging. I HIGHLY encourage everyone to read his paper for in depth details of his technique here.

As of today, IMPACT has been the only technique used for in vivo microscopy. Due to the complicated wavefront distortion encountered in highly scattering biological tissue, IMPACT has the highest success rate in enabling neuron imaging through intact skulls of adult mice. Through Dr. Cui's testing, he has proven that even with the unpredictable motion of awake mice, IMPACT using the segmented 492-DM were able to perform wavefront measurements and improve the image quality.

Dr. Cui used the BMC segmented 492-DM as both the wavefront modulation and correction device. The IMPACT measurement works by splitting the DM’s pixels and running parallel phase modulation with each actuator at a unique frequency. Modulating only a portion of the pixels while keeping the rest stationary, a linear phase shift is then used as a function of time over the entire 2π phase range. The unique modulation frequency then becomes the unique phase slope value. At the end of the modulation, a Fourier transform is used in IMPACT to determine the correction phase values. Dr. Cui then goes on to explain in detail how to determine what fraction of the pixels should be modulated, how to split the pixels into two evenly distributed groups and how the Nyquist-Shannon sampling theorem is integrated.

The imaging starts by setting the laser beam at the point of interest. The parallel phase modulation begins at one half at a time. As the measurement progresses, the laser focus becomes stronger, and laser power is gradually reduced to preserve the fluorescence signal from the sample. At the conclusion of the measurement, the compensated wavefront is displayed on the DM, and laser scanning in a conventional scope is begun. Figure 1 below shows the test setup for the experiment.

Figure 1. Setup of the multiphoton microscope integrated with IMPACT.

Dr. Cui used IMPACT for imaging the dendrites and spines of layer 5 pyramidal cells, in vivo at 650-670um under the dura in the mouse S1 cortex. In Media 1 below, you can see they are hardly resolvable with system correction only. In Media 2, you can see the dendrites and spines are clearly determined when full compensation has been applied.

For the first time, IMPACT enabled in vivo two-photon fluorescence imaging through the intact skull of adult mice. The technique also improved the fluorescence signal by a factor of ~20, along with overall resolution and contrast, this has proven to be a much greater adaptive optics imaging method than any other before. Dr. Cui also concluded that through these experiments, he found it worked well for awake, head-restrained animal imaging, providing a new and innovative solution for noninvasive studies of the mouse brain.

Before Deformable Mirrors became popular in the Adaptive Optics industry, consumers would generally turn to liquid crystal-based device (LCOS) spatial light modulators to confront their challenges. Here at BMC, we regularly receive questions on how all deformable mirrors, in addition to our MicroElectroMechanical (MEMS) deformable mirrors, compare to LCOS devices. Below I have touched upon some of the top differences between the two devices that I believe should play an important factor in one’s decision to purchase a wavefront shaping device.

1) LCOS devices are only available in a segmented architecture, where MEMS DMs offer both continuous and segmented styles in various styles and options. Although both layouts have their own advantages, most researchers favor the continuous model. Due to discontinuities between the actuators, it prevents any sharp edges within the image, making it well suited for imaging applications. Claire Max at UC Santa Cruz has explained and presented calculations on how you can achieve higher level of correction capability with a continuous mirror. Check out slide 47, which goes over her calculations here.

2) With MEMS DMs, we are able to offer strokes up to 5.5um (1.5um, 3.5um and 5.5um available), while LCOS SLMs are generally limited to only a stroke of 2PI in the visible region. This can be a major inconvenience for certain applications with higher amplitude aberrations.

3) The response time of our devices have always been much faster than any liquid crystal device on the market, while recent updates to our product line achieve even FASTER rates than before. Our devices can operate up to 60 kHz with our new high speed Kilo-S Driver or our Low-Latency Driver, whereas LCOS devices are limited to only a few hundred Hertz at best.

4) For the most part, LCOS devices are transmission based, causing light to be absorbed by the medium and resulting in lost light. There have been reflective devices introduced recently, however, they tend to scatter large amounts of light due to the small segment sizes. With a MEMS device, our segmented mirrors are over 98% reflective and our continuous mirrors are greater than 99%. Of course, this is the case only with the appropriate coating for the wavelength at which you are operating.

If you're interested in learning more about the differences between MEMS DMs and LCOS devices or the differences between any other mirrors currently on the market, please feel free to contact us here.

Scattering media can be a real headache if you are looking to achieve high-resolution, deep tissue in vivo images. Without adaptive optics, do not anticipate having the optical control you need to correct for scattering media effectively. But no need to worry, we have a solution.

Since standard Multiphoton Microscopy just wasn’t cutting it, the Cui Lab at Howard Hughes Medical Center pioneered a new technique that Boston University also recently developed, called Superpentation Multi-Photon Microscopy (S-MPM). Each group uses a different optimization scheme but the outcome is the same: The enhanced technique permits active compensation of wavefront aberrations in a scanning beam path through the use of a BMC MEMS Spatial Light Modulator (SLM), allowing for increased depth imaging.

Developed at Boston University and commercialized by Boston Micromachines, the enabling components are the Kilo-SLM and the high speed S-driver. With these components incorporated into the test bed shown in Fig. 1, images of 1 µm diameter fluorescent beads through 280 µm thick mouse skull can be achieved at depths of about 500 µm. The SLM corrected low order spherical aberrations as well as higher order scattering effects. Signal enhancement with higher resolution and contrast were improved by 10x-100x. The optimized SLM phase improves imaging over a field of view of 10-20 µm for samples tested to date with techniques currently in the works to improve upon this.

With 600 nm of stroke and 60 kHz of maximum frame rate, the Kilo-S System comes in a variety of options to fit your needs at a much reduced cost over our standard 1000 channel system. Contact us today for more information on our Kilo-S or any of our other systems!

About half of our customers use our deformable mirrors for laser applications, such as beam shaping or steering. We get a lot of questions pertaining to laser power and handling for both our deformable mirrors and modulators. Below is a summary of the guidelines we use when discussing our technolgy.

The most important specification to note immediately if you are working with lasers is the damage threshold of our DM's. There are two mechanisms of failure to consider: mirror damage due to heating and coating delamination. The first failure mode is largely governed by the average power experienced by the DM. The rule of thumb that we follow is maximum average power of 20W/cm². For the second failure mode, the peak energy is of greatest concern. In this case, the threshold that we use is that of a standard thin-film gold metallic coating, in this case, 0.4J/cm². Depending on the DM system, the calculations may be slightly different. In order to ensure a DM is suitable for your application, we typically need to know as many of the following properties as possible: the pulse width of the laser, peak power, frequency, wavelength and beam size. This last pameter will help to determine which aperture size is required and if you need to change your beam size at all. Additional information on laser power can be found on our previous blog here.

From a power threshold standpoint, our modulator technology works similarly to our deformable mirror technology. However, it may have a slightly lower damage threshold due to the fact that the exposed surface is a thin layer of silicon nitride as opposed to the thicker polysilicon surface used for our deformable mirrors. Honestly, we do not have much experience testing the devices. If you are interested in carrying out testing, we would be glad to lend you some modulators to test.

If you are interested in learning more about customers' experience with high-power lasers used on our DM's, pleaseclickhere to read Andrew Norton's paper on laser test performed using our DMs. Also, please visit ourwebsiteor contact usfor questions or additional information on how to obtain a device for testing.

For those interested in using our deformable mirrors with laser applications, there are a few common questions which are asked in regards to the AR-coated window and if it is/can be removable. Below is a summary of what's standard and what's possible:

Both the optical modulator and our DMs are protected by a 3mm thick window, which are standard BK-7 windows fromThorlabs. The options for windows are:

350-700nm

400-1100nm

650-1050nm

1050-1620nm

550nm-2400nm

This can also be customized upon request. The windows are mounted on a 6° angle in order to prevent ghosting.

A lot of requests are in regards to removing the protective window. For our standard DMs, the window is not removable as it is attached with an epoxy. For our modulators, the windowIS removable. We highly recommend youDO NOT REMOVE the protective window. The only exception to not having an AR-coated window would be if the DM was operated in a clean room environment. In this case, we can deliver the modulator or DM without the window and include a protective removable lid instead. In addition, we recommend flowing Nitrogen at a very slow pace around the mirror to ensure the humidity remains low around the DM. The required humidity is <30% as the mirror is made of polysilicon which needs to be protected from corrosion.

Just a few weeks ago we arrived back from the Photonics West 2014 exhibition and conference in San Francisco, CA. I wanted to share details and further observations on the show for those present at the show and those not being able to attend this year.

For the first time we made the decision to also attend the BiOS exhibition for the few days prior to PWest. Not being quite sure what to expect for booth traffic, especially since it conflicted with the superbowl, we still generated a good amount of interest for the smaller show. Our main presentations focused on our new adaptive optics-enhanced scanning laser ophthamoscope (AOSLO), the Apaeros Retinal Imaging System, which includes our Multi-DM, and the Superpenetration Multiphoton Microscopy technique, which is enabled by our Kilo-SLMand high speed S-Driver. Although both exhibits generated respectable notice and positive feedback, most people were familiar with the Superpentration Multiphoton work being done. Either wanting to try two-photon microscopy themselves or already in the process of doing so, our Kilo-SLM paired with our high speed S-driver presented data that was intriguing to most.

After wrapping up BiOS, we headed to the opposite side of the South hall at the Moscone Center for a larger booth setup for PWest. Here we had our entire mirror family on display, as well as live demonstrations of theReflective Optical Chopper and Wavefront Sensorless Adaptive Optics Demonstrator for Beam Shaping (WSAOD-B). For this part of the exhibition, I would say our deformable mirrors produced the most attention, most likely due to our wide assortment of shapes and actuator counts up to 4092. The WSAOD-B live demonstration did generate a great deal of attention, as most people are unaware of how sensorless AO works. Besides our deformable mirror line, I would still say the Multiphoton Microscopy overview was initiating even further interest here as well.

Overall BMC had a great show and it seemed well worth it to expand our exhibit onto BiOS beforehand. Although this was my first time attending the show, I noticed every inch of space at PWest being used for exhibitor tables and booths, even setting up in front of the bathrooms! I hope to see PWest advance even larger, maybe one day expanding to its third space, West Hall. I look forward to next year’s show and hope to reconnect with you all again throughout the year.

If you were not able to attend the show and would like any information on the products mentioned, please visit our websiteand download our whitepapers.

Happy New Year! Hope everyone had a great holiday and is staying warm.

To continue addressing our FAQ's, another recurring question BMC recieves is on the flatness of our deformable mirrors. The figure below shows an unpowered BMC DM and a flattened BMC DM.

The surface figure of our unpowered deformable mirrors has a low-order surface bow. The amount of stroke needed to flatten the DM is between .5 µm and 1 µm, depending on the model. We can guarantee that the stroke needed to flatten the deformable mirror will not exceed this amount and tends to be lower for the lower stroke devices.

However, researchers in the past have been able to achieve flattening the wavefront without using up any stroke on the DM. If you are able to include additional optics into your setup, the low order bow can be taken out with static optics. Just something to keep in mind as you are designing your system and trying to determine how much stroke is required to achieve your wavefront correction needs.

Over the past couple of months we have been receiving an assortment of questions in regards to our products. We thought it would be a good idea to share the more popular questions and answers as they stream in to keep everyone updated.

One question that tends to be asked quite often is the reflectivity our deformable mirrors can achieve. This depends on a couple of factors such as mirror coating, protective window AR coating and the wavelength of the light.

We offer gold, aluminum and protected silver coating on almost all of our deformable mirrors. When selecting a coating, you should pay particular attention to the wavelength(s) of light you use. The BMC DM Coating Reflectivity chart to the right illustrates the reflectivity of each of our standard coatings.

Our standard windows with AR coating are BK-7. We offer a few options, depending on which size mirror you select. For our smaller DMs, we offer the standard coatings from Thorlabs as well as a few more versatile options. You may choose either uncoated, 350-700nm, 650-1050nm or 1050-1620nm. We also offer a 400-1100nm window and 550-2400nm, the latter for an additional cost. For our larger DMs, various coating options are available. We do offer customizable options for an extra fee, so please contact us with your specifications if you require this.

The N-BK7 Broadband Antireflection Coatings chart fromThorlabsbelow depicts the percentage of light lost for each AR coated window. Similar curves are available for our other coatings.

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About the Author

Michael Feinberg is the Director of Product Marketing at Boston Micromachines Corporation. He has over 10 years of marketing and engineering experience in various technology fields. He can be reached at mrf@bostonmicromachines.com and welcomes any comments about the content presented herein.